After forming active device regions of a semiconductor device such as, for example, a diode, a transistor, a thyristor, or the like, in a semiconductor body (die) contact regions are formed, which contact the semiconductor body and allow to connect the semiconductor device to other devices in a circuit. Forming such contact regions may include depositing metallization layers on a surface of the semiconductor body to form conductive pathways. The most common metals used for this purpose are aluminium, or aluminium based alloys. Among several advantages, using an aluminium layer also has some drawbacks. For example, aluminium offers rather limited thermal and mechanical properties. Such disadvantages may be eliminated by using other metals instead of aluminium. Copper, for example, has a comparatively high thermal and electrical conductivity, and provides better contacts between the metallization layer and the bonding wires. Especially in SiC (silicon carbide) power semiconductor devices such as, for example, SiC-Schottky diodes, SiC-JFETs (Junction Field-Effect Transistors) or SiC-MOSFETs (Metal Oxide Semiconductor Field-Effect Transistors) the power cycling reliability may be improved.
To protect the semiconductor surface and the metallization layer from electrical and chemical contaminants or from humidity, for example, a passivation layer is deposited on the semiconductor substrate and on parts of the metallization layer. Those parts of the metallization layer, which are not covered by the passivation layer, can be contacted by bonding wires, for example. The semiconductor body is usually packaged and the package is filled with a mold compound or Silica gels. Most mold compounds and Silica gels, however, do not withstand high electric fields that may occur in the metallization layer. The passivation layer arranged on parts of the metallization layer, therefore, further serves to reduce electrical fields, especially in regions close to the metallization layer, to protect the mold compound. The passivation layer may include an imide. However, there are some materials, which are not compatible when arranged adjacent to each other. Imides, for example, are usually not compatible to copper.
Thus, if copper is used as a metallization layer and an imide is used as a passivation layer, the passivation layer needs to be separated from the metallization layer by a thin intermediate layer. Such an intermediate layer may include a nitride or aluminium oxide, for example. In a first step, the intermediate layer is usually deposited on the whole surface of the semiconductor substrate and of the metallization layer, and is, in a second step, removed from those parts of the semiconductor substrate, which are not covered by the metallization layer. Lots of materials, which may be used for the intermediate layer, however, may only be removed using a dry etch process. When the surface of a semiconductor body such as a SiC semiconductor body, for example, is exposed to a dry etch process, however, areas close to the surface of the semiconductor body may be negatively influenced. For example, impurities may be generated close to the surface, which may be charged or discharged during the operation of the device. This may lead to an unstable blocking behaviour of the device. This again may result in a reduction of the blocking voltage, which may cause a failure of the device.
There is therefore a need for a semiconductor device and a method for producing a semiconductor device with a passivation layer, which prevents a damage of the semiconductor body.